The field of the invention is fiber optic acoustic sensors (underwater fiber optic hydrophones), and more particularly in the desensitizing of certain sections of the optic fiber by means of a nickel jacket.
Fiber optic acoustic sensors have been described for use as underwater hydrophones. It is known that such optic fibers are acoustically sensitive, and can be made to have increased acoustic sensitivity by the use of compliant coatings. That is, the use of elastically compliant (low modulus) coatings on optical fibers is known to enhance their sensitivity to pressure/acoustic signals when used in interferometric fiber optic sensors.
For interferometric fiber optic sensors of this type, it is also desirable to have some fibers or some sections of fibers acoustically insensitive. Use of the same type analysis as used for compliant coatings to describe the use of higher elastic modulus coatings, such as electrodeposited nickel, shows that pressure and acoustic sensitivity is decreased by the higher elastic modulus coating. A typical required nickel coating or jacket thickness is predicted to be 10% to 30% of the optic fiber diameter, i.e. 10 to 20 .mu.m thickness for a 100 .mu.m diameter fiber.